When I arrange a scene with the camera at a low angle so that part of the ceiling shows, the ceiling is always black, as though unlighted. How,where do I place a light so that the ceiling shows?

WIP screenshot? Why can't you place a Spot light in the middle of the room, over your characte's heads, face up? Check if your lights are infinite or not. My guess is they are not, but if you're doing a room thing that may not make a differance...

the problem you have is that you dont have any light being cast on the ceiling. set an infinate light pointing at your scene at about the same angle as the camera. set the intensity low and tell it not to cast shadows and go into the material room and turn the specular color to black.

yes possibly shadow casting from a light above the ceiling also remember that seams show oddities unless the walls and ceilings are a single object definitely turn off all lighting above the ceiling